Method of chipping wood



Nov. 30, 1965 N. HARTLER ETAL 3,220,448

METHOD OF CHIPPING WOOD 3 Sheets-Sheet 1 Filed Dec. 2, 1963 Ni 15 HLPlI/er' Lanna/'2 Soo/{man w mhzz hw ATTORNEYS Nov. 30, 1965 N. HARTLER ETAL 3,220,443

METHOD OF CHIPPING WOOD Filed Dec. 2, 1963 3 Sheets-Sheet 2 INVENTORS Ni ls Hen He Lnndl"% SEOOk man BYJM ATTORNEYS Nov. 30, 1965 N. HARTLER ETAL 3,220,448

METHOD OF CHIPPING WOOD Filed. Dec. 2, 1963 3 Sheets-Sheet 5 Shear strength g 5 kg /crr1 Tang. surface Rad. surface part0 the fiber normal to the fiber 7 l 0 1.5 90 INVENTORS Ni ls H a r E lam Lanna! im/0mm ATTORNEYS United States Patent 3,220,448 METHOD OF CHIPPING WOOD Nils Hartler, Lidingo, and Lennart Stockrnan, Stockholm,

Sweden, assignors to Stiftelsen Svensk Celluloseforskning, Stockholm, Sweden, a corporation of Sweden Filed Dec. 2, 1963, Ser. No. 327,439 Claims priority, application Sweden, Dec. 5, 1962, 13,131/ 62 4 Claims. (Cl. 144326) The present invention relates to wood chipping, primarily for pulping but also for making particle board. The main object of the invention is to carry out the chipping operation so that the damage to the wood due to the chipping process is reduced and that the force necessary to achieve chipping is minimized.

In conventional chipping, feeding the wood piece, slicing it into discs of a length in the fiber direction equal to the chip length and simultaneously shearing such discs into chips are achieved by means of the forces of one and the same knife. The wood piece, usually a log, is fed through a spout to the rotating chipper disc which is provided with a number of knives. The position of the spout and its direction relatively to the chipper disc determine the cutting angle and also the angle between the projections on the plane of the disc of the main force vector and of the log axis.

In conventional chipping, the log is fed toward a point on the rotating chipper disc such that the projection on the plane of the disc of the main force vector extends substantially in parallel to the longitudinal axis of the log. According to the present invention, on the other hand, chipping is carried out in such a manner that the force vector in a plane (the cutting plane) through the cutting line (i.e. the line along which the cut develops in a given moment, said line coinciding with the edge of the knife) and parallel to the longitudinal axis of the log, is so directed that its component perpendicular to the fiber direction is considerably greater than the component parallel to the fiber direction. This means that the angle between the projections on the cutting plane of the main force vector and of the log axis is only slightly above 90. Furthermore, the angle between the cutting plane and the log axis shall be the least possible. This method of chipping involves considerable advantages which will be explained hereinafter.

The invention will be described more in detail with reference to the accompanying drawings.

FIGURE 1 shows diagrammatically a chipper disc and is intended to illustrate the effect of two different positionings of the spout.

FIGURES 2 and 3 illustrate the action of a knife in the two positions of the spout shown in FIGURE 1.

FIGURE 4 illustrates diagrammatically the chipping process.

FIGURE 5 is a graph which illustrates the relationship between the wood shear strength and the angle between the the fiber direction and the direction of the shear force.

FIGURE 6 is a diagrammatic view similiar to FIGURE 1 and illustrating the position of the spout in an embodiment of the invention.

Referring to FIGURE 1, there is shown a chipper disc with a few radial knives 16 shown in the lower part of the figure and in the upper right-hand quadrant two different positions of the log spout are illustrated by the elliptical cut surfaces 17 and 18 respectively of the log. The chipper is a right-hand machine, i.e. the disc 15 rotates in a clockwise direction. (If the rotation is in the opposite direction, the figure should be turned through the vertical plane. The disposition of the cut surface of the 10g on the disc plane is indicated by hours in accord ance with the usual convention which is also shown in FIGURE 1. A 3 oclock position (the surface 18) means an angle of 180 between the projection 19 (shown by a broken line) of the main force vector and the full line projection 20 of the log axis on the disc plane. In that case, the force acts parallel to the fiber direction and the chip formation occurs in the manner shown in FIGURE 2, where 25 is the log and 16 is the knife.

A 12 oclock position in FIGURE 1, as represented by the surface 17, is equivalent to an angle of between the broken line projection 23 of the main force vector and the full-line projection 24 of the log axis. In that case, the force acts perpendicular to the fiber direction, and the chip formation occurs as illustrated in FIGURE 3.

The chip formation (see FIGURE 4) can, in a simplified manner he considered as involving the step of shearing away a projecting portion 27 from an otherwise flat vertical wood piece 28. Chipping in the 3 oclock position is equivalent to applying a component 29 of the force vector parallel to the fiber direction, while chipping in the 12 o'clock position is equivalent to applying a force vector 30 normal to the fiber direction. Of course, any intermediate positions between these two extreme cases are possible. The force to be applied is equal to the product of the shear strength and the size of the surface exposed by the shearing operation. According to F. Kollmann, Technologie des Holzes under des Holzwerkstotfs', Munich 1951, the relationship between the wood shear strength and the angle between the fiber direction and the force vector is as illustrated by the graph in FIGURE 5. It will be apparent therefrom that shearing away the projecting portion 27 in FIGURE 4 by means of a force applied parallel to the fiber direction requires a considerably greater force than in the case of applying the force perpendicular to the fiber direction, as indicated by the values shown in FIGURE 4. Of course, these values are only intended to give a general idea of the magnitude of the forces and are not to be looked upon as exact values.

The forces occurring in connection with chipping results in a compression (crushing) of the wood which when it exceeds a certain minimum results in lowered quality characteristics of a pulp produced from the wood. This is particularly true in the case of sulfite pulp and is particularly relevant to the strength properties of the pulp. This minimum has been stated to be about 1% deformation by K. C. Logan, 0. J. K. Sepall, J. L. Chollet and T. B. Little (Pulp Paper Mag. Can. 61 (1960):ll, T515). J. E. Stone and L. S. Nickerson have shown (Pulp Paper Mag. Can. 59 (1958):6, that the loss n strength of sulfite pulp is greater when the same force 1s applied parallel to the fiber direction than in the case of applying it perpendicular to the fiber direction. In summary, this means that it is possible to compress up to a deformation of about 1% without causing any damage resulting in loss of strength properties of the pulp, but that such damage becomes more pronounced on further compression, an application of the force perpendicular to the fiber direction being considerably less harmful than parallel to the fiber direction.

In order to achieve the necessary feed of the log toward the chipper disc along the spout it is necessary that a sufficiently great force component is applied parallel to the log axis, i.e. in the fiber direction.

According to the present invention the component in the cutting plane of the main force from the knife is applied in such a direction that its component perpendicular to the fiber direction is predominating over the component parallel to the fiber direction, but at the same time the component parallel to the fiber direction is sufiiciently great to achieve the necessary feed of the log toward the chipper disc. To this end the log is fed in such a direction, i.e. the feed spout is so disposed, that the angle between the projections on the cutting plane of the main force vector and the longitudinal axis of the log is a little more than 90. This means, that in the example discussed, as illustrated in FIGURE 6, the cutting surface 31 of the log is positioned on the chipper disc with an angle a little over 90 between the projection 32 of the main shear force vector and the projection 33 of the log axis, which corresponds to a position of about 1 oclock of the cutting surface. In practice the angle between the projections referred to should be between 95 and 135.

To achieve fully the favourable effect illustrated in FIGURE 4, the spout angle, i.e. the inclination of the log axis to the cutting plane, should be the least possible. Theoretically this angle should be i.e. the log should be fed in a plane parallel to the cutting plane, which is of course impossible in practice. There is a practical lower limit for the spout angle, which will probably not be below Preferably the spout angle should be about 20 and not above 45.

By utilizing the cutting principle of this invention, as illustrated for a specific example by FIGURE 6, the force vector will be directed mainly perpendicular to the fiber direction, whereby two advantages are gained as compared to the case of applying the force substantially parallel to the fiber direction, namely that a lower force is required due to the lower shear strength of the wood in this loading case, and hence that the applied force results in less crushing of the wood and hence a reduced loss of strength of the resulting pulp than if the same force were directed parallel to the fiber direction. At the same time, however, the arrangement of FIGURE 6 permits a sufficient force parallel to the fiber direction to achieve the necessary movement of the log toward the cutting plane.

It will be appreciated that the arrangement of FIGURE 6 is only an example and represents the case where the spout extends in a vertical plane perpendicular to the chipper disc, i.e. the spout has no side angle. If the spout has a side angle, the optimum case will be changed as regards the disposition of the cutting surface so that the angle between the projections on the chipper disc of the main force vector and of the log axis is maintained. In the special case where the log is fed in a horizontal plane perpendicular to the chipper disc, the position of the cutting surface will be displaced clockwise from the 3 oclock position an angle equal to the displacement from the 12 oclock position in FIGURE 6, whereby the said angle will be equal in the two cases.

The sharpening angle of the knives and their mounting are no critical features of the present invention, but any conventional arrangement can be used. Similar to the conventional chipper principle, however, the sharpening angle of the knife should be as small as possible, which for reasons of strength means a sharpening angle of about 30 to 36. The knives should be mounted so that the clearance surface of the knife forms a sufiiciently great angle (clearance angle) with the cutting plane to achieve a satisfactory log clearance when the log is fed toward the knife.

Another advantage of the chips obtained by the method of this invention, apart from the reduced crushing, is that they are thinner than norm-a1 chips at equal length. In the case of sulfate pulping this means, that the cooking of the chips can be carried out with an improved uniformity. In practice this means that with an unchanged proportion of uncooked material, either the lignin content of the resulting unbleached sulfate pulp can be increased or the peak temperature used in the cooking can be increased. Both effects involve considerable advantages. In the former case an increased yield of pulp is obtained and in the latter case the cooking time is markedly shortened.

The invention is further illustrated by the following examples.

4 EXAMPLE 1 A pilot plant chipper was installed with a chipper disc diameter of 1.4 meters. A spout was mounted in a vertical plane perpendicular to the vertical chipper disc, i.e. with no side angle. The spout was positioned so that the cutting surface was in accordance with FIGURE 6, the angle between the projection of the main force vector and that of the log axis being The angle between the spout and the chipper disc (the spout angle) was variable and was varied in this experiment within the range of 10 to 42. The sharpening angle of the knives was 30 and their mounting such that the clearance angle was satisfactory for the necessary clearance (its magnitude is indicated for each run). The chipper disc was driven at a speed of 520 rpm. and the desired chip length was 25 millimeters.

In each run, an experimental spruce log was used, which was made by longitudinal cleavage of normal logs, whereby remaining portions of the starting logs could be used for making hand-prepared laboratory chips for comparison. Four runs were made and the resulting chips were tested by manual measurement of the dimensions and by sulfite cooking to a Roe number of about 6 on the unbleached sulfite pulp, beating in a PFI beater and strength testing. The latter tests were made in comparison to the mentioned corresponding laboratory chips and the strength testing results were evaluated as percent strength in relation to the strength of the laboratory chip pulp. This means that 0% designates absence of crushing damage and no strength loss due to thechipping and thus optimum chip quality. Table I below shows the chip dimensions and Table II shows the strength loss due to crushing damage.

Table I Spout Clearance Chip Chip Ratio of angle, angle, length, thickness, chiplength degrees degrees mm. mm. to chip thickness Table II Spout angle, Strength loss degrees on unbleached sulfite pulp,

percent Conventional industrial chips have a length to thickness ratio of between 5 and 7, which means that by the process of this invention, the chips obtained have a higher length to thickness ratio in the case of spout angles below 20 which are preferred according to this invention. It is probable that the length to thickness ratio is somewhat higher even at greater spout angles, although in that case the difference from conventional chips is much less. Normal industrial chips show a strength loss on unbleached pulp, when evaluated in the manner explained above, of approximately 15%. This shows that the chips made by the process of this invention are better, i.e. show less loss in strength, and this effect is greater as the spout angle is reduced. It is to be noted, however, that the effect is considerable when spout angles of up to 30 are used.

EXAMPLE 2 Chips prepared by the pilot plant chipper described in Example 1, using a spout angle of 18, and chips made in a conventional manner were subjected to sulfate cooking in a laboratory apparatus as described below.

70 grams of wood (dry basis) were Weighed and charged into autoclave tubes together with sulfate cooking liquid in a liquid to wood ratio of 4: 1. The amount of chemicals was such that the desired Roe number was achieved within a cooking period of 2 hours, and the sulfidity was 25%. The cooking liquid was preheated to 70, whereupon the temperature was raised to the desired peak temperature at a rate of 1 C. per minute. The cooking period at peak temperature was 2 hours. After interruption of the cook, the resulting pulp was washed in hot water and was then screened in a water jet defibrator, model NAF, at a water pressure of 1.5 atmospheres and having circular perforations in the screen annulus of 2 millimeters. The amount of pulp which does not pass through the perforations is designated as knots and is determined separately.

The Roe number and yield of the resulting pulp were determined. The Roe number achievable and the peak temperature which could be used to obtain a maximum of 1% knots were determined. The following results were obtained.

It is apparent from this table that from chips prepared by the process of this invention it is possible to make pulp having a higher Roe number and to use a higher peak temperature without increasing the amount of knots. This means in practice that due to the quality of the chips prepared by the present process the sulfate cooking has resulted in a more uniform delignification. From a practical point of view, it means also that pulp prepared from chips made by the present process, can be prepared with a higher Roe number, i.e. a higher yield, or can be cooked with a higher peak temperature which means a more rapid cooking.

We claim:

1. A method of making wood chips, which comprises feeding a log toward the cutting plane so that a force vector in a plane through the cutting line and parallel to the longitudinal axis of the log has such a direction that its component perpendicular to the fiber direction is predominating over the component parallel tothe fiber direction, the angle between the projections on the cutting plane of the main force vector and of the log axis being only a little above and the angle between the cutting plane and the log axis is the least possible.

2. A method as in claim 1, in which the angle between the projections of the main shear force vector and the log axis on the cutting plane is to 3. A method as in claim 1 in which the log is fed in a vertical plane perpendicular to the cutting plane.

4. A method as in claim 1 in which the log is fed in a horizontal plane.

References Cited by the Examiner UNITED STATES PATENTS 10/ 1953 Clark.

8/1959 Schubert 144-172 

1. A METHOD OF MAKING WOOD CHIPS, WHICH COMPRISES FEEDING A LOG TOWARD THE CUTTING PLANE SO THAT A FORCE VECTOR IN A PLANE THROUGH THE CUTTING LINE AND PARALLEL TO THE LONGITUDINAL AXIS OF THE LOG HAS SUCH A DIRECTION THAT ITS COMPONENT PERPENDICULAR TO THE FIBER DIRECTION IS PREDOMINATING OVER THE COMPONENT PARALLEL TO THE FIBER DIRECTION, THE ANGLE BETWEEN THE PROJECTIONS ON THE CUTTING PLANE OF THE MAIN FORCE VECTOR AND OF THE LOG AXIS BEING ONLY A LITTLE ABOVE 90* AND THE ANGLE BETWEEN THE CUTTING PLANE AND THE LOG AXIS IS THE LEAST POSSIBLE. 